Particle concentration detector

ABSTRACT

An apparatus in which a concentration of toner particles in a mix of carrier granules and toner particles is detected permitting the regulation thereof. A voltage gradient is impressed upon a reflecting surface and a beam of light rays illuminates a portion of the surface having a pre-selected potential thereon. The intensity of the light rays reflected from the illuminated portion is sensed and an electrical output signal generated. This electrical output signal is a measure of the toner particles deposited on the illuminated portion which indicates the concentration of toner particles within the mix. The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as to the scope of the invention in any way.

United States Patent [191 Davidson Mar. 25, 1975 PARTICLE CONCENTRATIONDETECTOR Primary Examiner-Mervin Stein Assistant ExaminerLeo Millstein[75] Inventor James Davidson Rochester Attorney, Agent, or Firm-J. J.Ralabate; H. Fleischer; [73] Assignee: Xerox Corporation, Stamford, C A,Green Conn.

22 Filed; Aug. 6, 1973 1 ABSTRACT [21] AppL NO: 385,936 An apparatus inwhich a concentration of toner part cles 1n a mix of carrler granulesand toner particles is detected permitting the regulation thereof. Avoltage [52] U.S. Cl 118/7, ll8/9, ll8/l0, gradient is impressed upon areflecting surface and a 355/3 beam of light rays illuminates a portionof the surface [51] Int. Cl G03g 13/00 having a pre-selected potentialthereon. The intensity [58] Field of Search 118/4, 7, 9, 10, 637; of thelight rays reflected from the illuminated portion 117/ 17.5; 355/3 DD issensed and an electrical output signal generated. I This electricaloutput signal is a measure of the toner [56] References Cited particlesdeposited on the illuminated portion which UNITED STATES PATENTSindicates the concentration of toner particles within 3,348,521 10/1967Hawk 118/7 the 3,430,606 3/l969 Pease et a] 118/637 The foregoingabstract is neither intended to define 3.727.065 4/1973 the inventiondisclosed in the specification, nor is it 3,765,654 l0/1973 intended tobe limiting as to the scope of the invention 3,791,744 2/l974 i any way3,80l l96 4/1974 Knapp et al 355/3 22 Claims, 6 Drawing Figures 1 6 4 al 3 6/56 aa PM'EHTEU SHEET 1 OF 2 1 PARTICLE CONCENTRATION DETECTORBACKGROUND OF THE INVENTION This invention relates generally to amulti-color electrophotographic printing machine, and more particularlyconcerns an apparatus for regulating the concentration of tonerparticles within a developer mix of carrier granules and toner particlesemployed in the development system thereof.

The concentration of toner particles within the developer mix directlyaffects the quality of reproduction created by the multi-colorelectrophotographic printing machine. Toner particle concentrationrelates directly to the characteristics of the developed image. Forexample, the density and color balance of the image may be affected bythe concentration of toner particles within the developer mix.

Various types of systems have been developed which add toner particlesto the developer mix. However, the majority of these systems donot-monitorthe concentration of toner particles within the mix.Recently, systems have been developed which detect the concentration oftoner particles within the mix and provide additional toner particlesthereto as required. Most of the foregoing types of systems are directedto black and white printing machines rather than multi-color printingmachines.

A typical system utilized in a black and white printing machine isdisclosed in U. S. Pat. No. 3,399,652 issued to Gawron in 1958. Gawrondescribes a rotating disc positioned in a developer mix. The disc iselectrically biased to attract toner particles from the mix. A lightbeam is reflected from the surface of the disc onto a photoelectricunit. The intensity of the light rays striking the photoelectric unit isan indication of the density of toner particles deposited on the disc,which, in turn, corresponds to the toner particle concentration withinthe developer mix.

Another system employed in a black and white electrophotographicprinting machine is disclosed in U.S. Pat. No. 3,094,049 issued toSnelling in 1963. Snelling describes a plate having a conductive filmwith a pattern inscribed thereon. The pattern is electrically biased toattract toner particles thereto simulating an image being developed.Light rays are transmitted through or reflected from the toner particlesto indicate the density of toner deposited thereon. The density of tonerparticles adhering to the plate corresponds to the concentration oftoner particles within the developer mix. However, the Snelling patentis directed primarily to edge development and does not address theproblem of extending this technique to electroded or magnetic brushdevelopment wherein the entire solid area is developed.

One system adapted for use in a multi-color electrophotographic printingmachine is described in copending application Ser. No. 213,056, filed in1971, U.S. Pat. No. 3,754,821. As disclosed therein, the apparatusincludes a transparent electrode mounted on the photoconductive memberand adapted to attract electrostatically toner particles thereto. Alight source generates a beam of light rays which are transmitted fromthe interior of the photoconductive drum through the transparentelectrode onto a photosensor. The photosensor develops an electricalsignal indicative of the density of toner particles adhering to thetransparent electrode. In the foregoing system, light rays pass throughthe transparent electrode rather than being reflected therefrom.

The problem of detecting toner particle concentration within adevelopment system having solid area capability is appreciably moredifficult than one wherein the system has only edge developmentcapability. In a solid area system, the light rays reflected from asurface having toner particles deposited thereon may be totally cut offby toner particles which are slightly separated from each other. Thus,the deposition of additional toner particles will have no effect in thelight rays reflected therefrom. A detection system of this type ishighly sensitive to a low degree development as compared to nodevelopment. However, it possesses little ability to differentiatebetween varying higher degrees of development. This type of system iseffective for detecting edge development but has little ability todetermine toner concentration in solid area development. In solid areas,the regulating apparatus may need to distinguish between a density of0.8 and one of 0.9. The intensity of the light rays reflected from atoner powder image havinga 0.8 density and a toner powder image having a0.9 density would be substantially identical, and the system may beincapable of detecting a difference therebetween.

Accordingly, it is a primary object of the present invention to improvethe apparatus used to regulate toner particle concentration within adeveloper mix employed in a development system having solid areacapability.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with thepresent invention, there is provided an apparatus for regulating theconcentration of toner particles in a mix of carrier granules and tonerparticles.

Pursuant to the present invention, reflecting means is disposed toattract toner particles thereto from the carrier granules of the mix.Means are provided for biasing electrically the reflecting means toproduce thereon a voltage pattern having a greater potential in a firstregion than in a second region thereon. Generating means produce a beamof light rays. The reflecting means is in a light-receiving relationshipso that a third region thereof having a potential intermediate thepotential of the first region and second region is illuminated by thebeam of light rays. Detecting means measure the intensity of the lightrays reflected from the re-.

flecting means. The detecting means produce an electrical output signalindicative of the density of toner particles deposited on theilluminated portion of the reflecting means.

Further in accordance with the present invention, an alternateembodiment thereof utilizes means for recording a sample electrostaticlatent image on a photoconductive member of an electrophotographicprinting machine. A voltage gradient is impressed on the sampleelectrostatic latent image such that the potential thereof decreasesfrom a first potential to a second potential. As previously described,generating means produce a beam of light rays. The light rays illuminatea portion of the sample electrostatic latent image having a pre-selectedpotential intermediate the first and second potential. The intensity ofthe light rays reflected from the illuminated portion of the sampleelectrostatic latent image is detected. An electrical output signal isgenerated. indicative of the density of toner particles 3 deposited on"the illuminated portion of electrostatic latent image.

BRIEF DESCRIPTION or THE DRAWINGS the sample features of the presentinvention therein;

FIG. 2 is a fragmentary plan view of the regulating apparatus of thepresent invention;

FIG. 3 is a perspective view of the reflecting means employed in theFIG. 2 regulatory apparatus;

FIG. 4 is a fragmentary plan view of the reflecting means andelectricalbiasing employed in the FIG. 2 regulating apparatus; I

FIG. 5 is a schematlcplan view of the development system usedin the FIG.1 printing machine; and

FIG. 6 is a perspective view of the modification required in the FIG.lprinting machine toproduce a sample electrostatic latent image.

1 While the present invention will be described in connection with apreferred embodiment thereof, it will be understood that it is notintended to limit the invention to that embodiment. On the contrary, itis intended to cover all alternatives, modifications and equivalents asFirst, drum 10 rotates photoconductive surface 12 through chargingstation A. At charging station A, a corona generating device, indicatedgenerally at'16, extends longitudinally in a transverse direction acrossphotoconductive surface 12."-The corona-generating device 16 produces aspray of ions for charging photoconductive surface 12 to a substantiallyuniform potential. US. Pat. No. 2,778,946 issued to Mayo in 1957describes a suitable corona generating device of the type which may beutilized herein.

Thereafter, drum 10 rotates the charged photoconductive surface toexposure station B. At exposure station B, a color-filtered light imageoforiginal document may be included within the spirit and scope of theinvention' as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION With continued reference to thedrawings wherein like reference numerals have been used throughout toindicate like elements, FIG. 1 depicts a multi-color electrophotographicprinting machine in which the present invention may be incorporated. Thevarious components of the multi-color printing machine are illustratedschematically in FIG. 1.Although the regulating apparatus of the presentinvention isparticularly well adapted for use in this type of anelectrophotographic printing machine, it should become evident from thefollowing discussion that it is equally wellsuited for use in a widevariety of electrostatographic printing machines, andis not necessarilylimited in its use to the particular embodiment shown herein.

Turning now to FIG. 1, the electrophotographic printing ma'chingdepicted therein employs an imagebearing member comprising a drum 10having a photoconductive surface 12 secured to the exteriorcircumferential surface thereof. Drum 10 is mounted rotatably of themachine frame and driven at a substantially constant angular velocity,in the direction of arrow 14, by a drive motor (not shown). One type ofsuitable photoconductive material is disclosed in US. Pat. No. 3,655,377issued to Sechak in 1972. A series of processing stations aredisposedabout the periphery of drum 10 such that as it rotates in the directionof arrow 14, photoconductive surface 12 passes sequentiallytherethrough. The drive motor rotates drum 10 at a predetermined speedrelative to the other operating mechanisms of the printing machine. Atiming disc mounted in theregion of one end of the shaft of drum 10cooperates with the machine logic to synchronize the various operationswith the rotation of drum 10. In this manner, the proper sequence ofevents is produced at the respective processing stations.

18 is projected onto charged photoconductive surface 12. Exposurestation B includes a moving lens system, generally designated by thereference numeral 20, and a color filter mechanism indicated generallyas 22. As

' shown in FIG. 1, original document 18, such as asheet of paper, .bookor the like, is placed face down upon transparent viewing platen 24.Lamp assembly 26, lens syste'l'n 18 and filtermechanism 20 are moved ina timed relation with drum 10 to scan successive longitudinallyextending incremental areas of original document 18 disposedupon platen24. In this manner, a flowing light image of original document 18 isprojected onto chargedphotoconductive surface12. During exposure, filtermechanism 22 interposes selected color filters into the optical lightpath of lens 20. The filter operates on the light rays passing throughlens 20 to record an electrostatic latent image on photoconductivesurface 12 corresponding to a pre-selecte'd spectral region of theelectromagnetic wave spectrum-- hereinafter referred to as a singlecolor electrostatic latent image. A suitable moving lens system isdisclosed in US. Pat. No. 3,062,108 issued torMayo in 1962.

After the single color electrostatic latent image is recorded onphotoconductive surface 12, drum 10.rotates to development station C.Development station C includes three individual developer unitsgenerally indicated by the reference numerals 28, 30, and 32,respectively. The developer units are all of a type referred to in theart as magnetic brush developer units. In a magnetic brush developerunit, a magnetizable developer mix having carrier granules and tonerparticles is continually brought through a directional flux field toform a brush of developer material. The developer mix is continuallymoving to provide fresh developer mix to the brush. Preferably, themagnetic brush system comprises a magnetic member with a mass ofdeveloper mix adhered thereto by magnetic attraction. The developer mixincludes carrier granules having toner particles clinging thereto bytriboelectric attraction. This chainlike arrangement of developer mixsimulates the fibers of a brush. Development is achieved by bringing thebrush of developer mix into contact with the electro-. static latentimage recorded on photoconductive surface 12. Each of the developerunits 28, 30, and 32, respectively, apply toner particles to theelectrostatic latent image recorded on photoconductive surface 12 whichis adapted to absorb light within a pre-selected spectral region of theelectromagnetic wave spectrum corresponding to the wavelength of lighttransmitted through filter 22. For example, a latent image formed bypassing the light image through a green filter will record the red andblue portions of the spectrum as areas of relatively high chargedensityon photoconductive through the filter and cause the chargedensity on photoconductive surface 12 to be reduced to a-voltage levelineffective for development. The charged areas are then made visible byapplying green absorbing magenta toner particles to the latent imagerecorded on photoconductive surface 12. Similarly, a blue separation isdeveloped with blue absorbing yellow" toner particles, while the redseparation is developed with red absorbing cyan toner particles. Thedevelopment system will be further described withreference to FIG. 5.

Pursuant tothe present invention, additional toner particles are addedto the respective developer mixes when the concentration thereof isreduced beneath a specified level. The toner particle concentration isdetermined by the regulating apparatus of the present invention,indicated generally at 34. Regulating apparatus 34 includes reflectingmeans, indicated generally at 36, mounted on photoconductive surface 12of drum in the non-image area thereof. Generating means or light source38, illuminates a portion of reflecting means 36. The light raysreflected from reflecting means 36 are detected by detecting means orphotosensor 40. As the electrostatic latent image recorded onphotoconductive surface 12 is developed, toner particles are depositedon reflecting means 36. The intensity of the light rays reflected fromreflecting means 36 in the illuminated area is indicative of the densityof toner particles deposited thereon. Photosensor 40 is positioned in alight receiving relationship with the light rays reflected fromreflecting means 36. In this way, the density of toner particlesdeposited on reflecting means 36 is sensed by photosensor 40 and theelectrical output therefrom corresponds thereto. It should be noted thatthe density of the toner particles deposited on reflecting means 36 isindicative of the concentration of toner particles within the developermix. The detailed structural configuration of regulating apparatus 34will be described hereinafter in greater detail with reference to FIGS.2 through 4, inclusive.

Continuing now with the description of the various processing stationsemployed in the multi-color electrophotographic printing machine of FIG.1, after development, drum 10 rotates photoconductive surface 12 totransfer station D. At transfer station D, the toner powder imageadhering electrostatically to photoconductive surface 12 is transferredto a sheet of support material 42. Final support material 42 may be,amongst others, plain paper or a sheet of polysulfone thermoplasticmaterial. A transfer roll, shown generally at 44, secures supportmaterial 42 releasably thereto for movement therewith in a recirculatingpath. Transfer roll 44 rotates in the direction of arrow 40, insynchronism with drum 10 (in this case at substantially the same angularvelocity). Transfer roll 44 is biased electrically to a potential havingsufflcient magnitude and the proper polarity to attractelectrostatically toner particles from the latent image recorded onphotoconductive surface 12 to-support material 42. A suitableelectrically biased transfer roll is described in U.S. Pat. No.3,612,677 issued to Langdon et al. in 1971. Transfer roll 44 includes arecess therein arranged to prevent contact with the toner particlesdeposited on reflecting means 36. Thus, the toner particles depositedthereon are not disturbed by the transfer process and represent a trueindication of the toner particle concentration within the developer mix.

After a plurality of toner powder images have been transferred fromphotoconductive surface 12 to support material 42, support material 42is separated from the surface of transfer roll 44 and advanced to afusing station (not shown). At the fusing station, the toner powderimage is permanently affixed to support material 42. One type ofsuitable fuser is described in U.S. Pat. No. 3,498,592 issued to Moser,et al. in 1970. After the fusing process, support material 42 isadvanced by a plurality of endless belt conveyors (not shown) to a catchtray (not shown) for subsequent removal therefrom by the machineoperator.

Although a preponderance of toner particles are transferred to supportmaterial 42, invariably some residual toner particles remain onphotoconductive surface 12 after the transfer of the toner powder imageto support material 42. These residual toner particles are removed fromphotoconductive surface 12 as it passes through cleaning station E. Atcleaning station E, the residual toner particles are initially broughtunder the influence of cleaning corona generating device (not shown)adapted to neutralize the remaining electrostatic charge onphotoconductive surface 12 and the residual toner particles. Thereafter,the neutralized toner particles are cleaned from photoconductive surface12 by a rotating fibrous brush 48. Brush 48 is positioned in contactwith photoconductive surface 12. One typeof suitable brush cleaningdevice is described in U.S. Pat. No. 3,590,412 issued to Gerbasi in1971.

It is believed that the foregoing description is sufficient for purposesof the present application to illustrate the general operation of themulti-color electrophotographic printing machine embodying the teachingsof the present invention therein.

Referring now to the specific subject matter of the present invention,FIG. 2 illustrates in a plan view the detailed construction ofregulating apparatus 34. As hereinbefore indicated, regulating apparatus34 includes reflecting means 36, light source 38 and photosensor 40. Inaddition, each of the developer units 28, 30, and 32, respectively, havea corresponding toner particle storage container associated therewith.As shown in FIG. 2, light source 38 produces a beam of light rays whichare reflected from reflecting means 36 to photosensor 40. Reflectingmeans 36 is located on a non-image portion of photoconductive surface12'. As reflecting means 36 passes through the development zone, tonerparticles are attracted thereto. Light source 38 illuminates a portionof reflecting means 36, reflecting means 36 having a voltage gradientthereacross.

Turning now to the specific structural configuration of reflecting means36, reflecting means 36 includes a plurality of conductive layers 50,52, and 54, respectively. Conductive layers 50, 52, and 54 are spacedfrom one another and electrically coupled to one another by resistancelayers 56 and 58. The entire assembly is secured to insulating layer 60.Resistance layer 56 and 58 are reflective and adapted to reflect thelight rays from light source 38 to photosensor 40.

As shown in FIG. 3, conductive layers 50 and 52 are disposed in themarginal regions of reflecting means 36 while conductive layer 54 isdisposed in the central portion thereof. By way of example, insulatingsupport means may be an epoxy coated glass member. Conductive layers 52,54, and 56 may be aluminum evaporated onto insulating support 60.Resistance layer 56 conductive layers and 58 are an electricallyresistant coating secured to insulating layer 60.

Referring now to FIG. 4, there is shown the electrical biasing circuitryfor reflecting means 36. As shown therein a high voltage source 62 isconnected to conductive layers 50 and 52. A low voltage source 64 isconnected to conductive layer 54. In operation, voltage source 64 may beadjusted to apply the same voltage to conductive layer 54 as is appliedto the magnetic brush development system. For example, the developerbias may be about 500 volts. Under these circumstances power supply 64would be similarly adjusted to about 500 volts.. Contrawise high voltagesource of power supply 62 would be adjusted to a substantially highervalue, for example, about 900 volts. In this manner, a current flow isdevelopedin resistance layers 56 and 58 to produce a voltage gradientdecreasing inwardly from 50 and 52 to-conductive layer 54. Light source38 is adapted to illuminate a selected region of resistance layer 56 orresistance layer 58 having a selected voltage value. By way of example,light source 38 may illuminate a region of resistance layer 56 having avoltage of about 750 volts. Toner particles will be attracted from themagnetic brush system to the regions of resistance layers 56 and 58having a potential greater than the magnetic brush potential. However,the amount of toner concentration of toner particles within thedeveloper mix will determine the amount of toner particles attractedthereto. Thus, for example, if few toner particles are attracted to theregion being illuminated by light source 36 i.e., the portion ofresistance layer 56 having a potential of about 750 volts, tonerconcentration within the developer mix is too low and additional tonerparticles have to be added thereto from the toner particle storagecontainer. However, if relatively many toner particles are deposited onthe illuminated area, toner particle concentration within the developermix is satisfactory and no toner particles need'be added to thedeveloper mix. Thus, the circuit arrangement in conjunction with thereflecting means 36 is an ON/OFF type of controller, wherein thedeposition of toner particles on .the illuminated region prevents theaddition of tonerparticles to the developer mix. Contrawise,-the absenceof toner particles from the illuminated region indicates that tonerparticles must be added to the developer mix. It is evident that thebiasing voltage applied to reflecting means 36 may be suitably adjustedmerely by adjusting the respective power supplies 62 and 64. In thismanner, a variable voltage gradient may be produced on resistance layers56 and 58 to produce the desired voltage pattern. In operation, it ispreferred that the system operate such that when toner particles aredeposited on the'illuminated portion of the reflecting means, noadditional toner particles are required in the development mix; whereaswhen no toner particles are deposited in the illuminated portion,additional toner particles are required in the developer mix.

Referring now to FIG. 5, there is shown developer units 28, 30, and 32respectively in detail. Power supply 65 regulates'the electricalpotential applied to the respective developer rolls 68, fore described,power supply 64 (FIG. 4) electrically biasing resistance element 54 isadjustable so as to substantially match the electrical biasing potentialapplied to developer rolls 68, 70, and 72 by power supply 65. Ifdesired, power supply 64 and power supply 65 may 70, and 72. Ashereinbebe a common power supply rather than two separate powerssupplies. Each of the developer units 28, 30, and 32 are substantiallyidentical, therefore, only development unit 28 will be briefly describedhereinafter. The developer mix is carried from the sump of developerunit 28 by a paddle wheel (not shown) to a transport roll (not shown)and then to developer roll 68 which is positioned closely adjacent tophotoconductive surface 12 of drum 10. Developer roll 68 includes anon-magnetic tubular. member, preferably made from aluminum having anirregular or roughened exterior surface. The tubular member is journaledfor rotation by suitable means such as ball bearing mounts. A shaft madepreferably of steel is concentrically mounted within the tubular memberand serves as a fixed mounting for magnets. The magnets are bariumferrite in the form of angular ringsand arranged with five poles onabout a 284 arc about the steel shaft. The developer mix is brought intocontact with the developer roll which in turn moves it into contact withthe electrostatic latent image recorded on photoconductive surface 12and recording means 36. Toner particles are attracted to recording means36 from' the carrier granules attached magnetically to developer roll68.

Each of the developer units 28, 30, and 32, respectively, have acorresponding toner particles storage container associated therewith.The toner particle storage container has a supply of toner particleshaving discrete colors to form a reservoir thereof for the appropriatedeveloper unit. By way of example, the toner particle storage containerfor developer unit 28 has cyan toner particles, that of developer unit30, magenta toner particles, and that of developer unit 32 yellow tonerparticles. Each of the toner particle storage containers includeperforations therein adapted to meter therefrom a specified quantity ofthe selected toner particles to the corresponding developer unit. Asuitable oscillator motor vibrates the appropriate toner particlestorage container to dispense toner particles therefrom. The tonerparticles pass through the perforations in the container to thecorresponding developer unit. Regulating apparatus 34 actuates theoscillator motor to control the dispensing of toner particlesfrom eachof. the toner particle storage containers to the respective developerunit.

By way of example, suitable logic circuitry processes the electricaloutput signalfrom photosensor 40. The logic circuitry, preferably,includes a suitable discriminator circuit arrangedto compare a referencewith the electrical output signal from photosensor 40. The discriminatorcircuit may utilize a silicon control switch which turns on andeffectively locks in after an electrical output signal having amagnitude greater than the reference is obtained. The signal from thediscriminator circuit changes the state of the flip-flop todevelop anoutput signal therefrom. The output signal from the flip-flop, inconjunction with an output signal from the appropriate developer unitactuates an AND gate which, in turn, transmits a control signal to theoscillator motor of the toner particle storage container housing thetoner particles corresponding to the developer unit generating theoutput signal to the AND gate. The control signal also resets theflip-flop. This type of logic circuitry is on/off. Thus, when theintensity of the light rays reflected from the illuminated portion ofreflecting means 36 is diminished due to toner particles being depositedthereon, electrical output signal from photosensor 40 is reduced. Whenthe electrical output signal from photosensor 40 is reduced beneath thepreselected reference, the oscillator motor of the appropriate tonerparticle storage housing is de-energized preventing the dispensing oftoner particles therefrom. Contrawise, when no toner particles aredeposited on the illuminated region of reflecting means 36, the intensity of the light rays reflected therefrom is not diminished and theelectrical output signal from photosensor 40 is greater than thereference. Under these circumstances, the appropriate oscillator motorof the respective toner particle storage container is energizeddispensing toner particles therefrom into the developer mix. Thus, thetoner particle concentration Within each of the respective developermixes may be adjusted independently and relative to one another.

An alternate embodiment to the previously discussed apparatus utilizes asample electrostatic latent image recorded on photoconductive surface12. The sample electrostatic latent image has a voltage gradient thereonrather than on reflecting means 36 hereinbefore described. FIG. 6illustrates a modification to the multicolor electrophotographicprinting machine described in FIG. 1 which enables a sampleelectrostatic latent image to be recorded on photoconductive surface 12.As shown in FIG. 6, a disc 66 having a plurality of variable densitysamples (in this case three) disposed thereon is mounted rotatablybeneath transparent platen 24. Disc 66 is mounted rotatably in theprinting machine and is positioned beneath transparent platen 24 withinthe half angle of the optical system. Before Lamps 26 begin to scan,they are actuated to illuminate one of the variable density samples. Inthis manner, a sample electrostatic latent image is recorded onphotoconductive surface 12 as drum 10 rotates. Lamps 26 are stationaryand the appropriate filter is positioned in filter 22 forming a sampleelectrostatic latent image on photoconductive surface 12 which is adischarged strip having the desired potential gradient thereon.Preferably, disc 66 includes three equally spaced variable densitysamples located about the periphery thereof. Sample 68 is a variabledensity sample for a green separation, sample 70 is a variable densitysample for red separation and sample 72 is a variable density sample forthe blue separation. Each of the variable samples has a color gradientthereacross so that the intensity of the light reflected therefromvaries across the variable density sample. Thus, the intensity of thelight irradiating charged photoconductive surface 12 will vary todischarge photoconductive surface 12 in accordance therewith.Preferably, the voltage gradient produced on photoconductive surface 12decreases in the direction of rotation of drum 10 as indicated by arrow14. Thus, toner particles are attracted to the areas of the sampleelectrostatic latent image having a greater charge than the magneticbrush developer bias. Once again, toner particles are attracted to thesample electrostatic latent image forming a toner powder gradientthereon. As drum 10 rotates, light source 38 illuminates the developedsample electrostatic latent image. The intensity of the light raysreflected therefrom is continually detected by photosensor 40. Theelectrical output signal from photosensor 40 is compared with thereference. Hence, the electrical output signal from monitored. If thistime interval exceeds a pre-selected 6 photosensor 40 increases as afunction of time. The

time interval required for the electrical output signal from photosensor401p exceed a selected reference is time reference, toner particles arenot added to the developer unit, whereas if the time interval is lessthan the pre-selected time reference, toner particles are added to thedeveloper unit.

In recapitulation, a regulating apparatus has been disclosed wherein areflecting means having a voltage gradient thereon is mounted on aphotoconductive surface to attract toner particles thereto. Moreover, analternate embodiment utilizes a sample electrostatic latent image havinga voltage gradient thereon. In both of the foregoing instances, thedensity of the toner particles attracted thereto is dependent upon thevoltage of either the reflecting means or the sample electrostaticlatent image. A light source illuminates the reflecting means or sampleelectrostatic latent image and the intensity of the light rays reflectedtherefrom is detected by a photosensor. Suitable circuitry is associatedwith the photosensor to develop an electrical output signal arranged toenergize the appropriate toner particle storage container to dispensetoner particles therefrom. The toner particles replenish the depletedsupply thereof in the respective developer mix. in this way, the tonerparticle concentration within the developer mix is maintainedsubstantially constant to insure that the density and color balance offthe multicolor reproduction is substantially optimized.

It is, therefore, evident that there has been provided, in accordancewith the present invention an apparatus for regulating the concentrationof toner particles within a developer mix employed in a developmentsystem of a multi-color electrophotographic printing machine that fullysatisfies the objects, aims, and advantages set forth above. While thisinvention has been described in conjunction with specific embodimentsthereof, it is evident that many alternatives, modifications andvariations will be apparent to those skilled in the art. Accordingly, itis intended to embrace all alternatives, modifications and variationsthat fall within the spirit and broad scope of the appended claims.

What is claimed is: 11. An apparatus regulating toner particleconcentration within a mix of toner particles and carrier granulesemployed in a development system arranged to deposit toner particles onan image-bearing member, including: reflecting means disposed to attracttoner particles thereto from the carrier granules of the mix;

means for biasing electrically said reflecting means to produce avoltage pattern having a greater potential in a first region of saidreflecting means than in a second region thereof;

means for generating of a beam of light rays, said refleeting meansbeing in a light receiving relationship with the beam of light rays sothat a third region thereof having a preselected potential intermediatethe potential of the first region and second region is illuminated bythe beam of light rays; and

means for detecting the intensity of the light rays reflected from saidreflecting means, said detecting means producing an electrical outputsignal indicative of the intensity of light ray reflected from saidreflecting means.

2. An apparatus as recited in claim 1, further including means,responsive to the electrical output signal from said detecting means,for dispensing toner particles into the mix of the development system tomaintain the concentration thereof at substantially about the desiredlevel. I

3. An apparatus as recited in claim 1, wherein said reflecting meansincludes:

insulating support means;

a pair of conductive layers mounted on said support means, one of saidpair of conductive layers being positioned in the first region of saidreflecting means and the other of said pair of conductive layers beinglocated in the second region thereof; and

a resistance layer mounted on said support means connecting electricallysaid pair of conductive layers with one another.

4. An apparatus as recited in claim 3, wherein said electrical biasingmeans includes:

a first voltage source electrically coupled to said one of said pair ofconductive layers disposed in the first region of said reflecting means;and

a second voltage source electrically coupled to said other of said pairof conductive layers disposed in the second region of said reflectingmeans, said second voltage source generating a greater potential thanthe potential generated by said first voltage source to create a currentflow from said other of said pair of conductive layers to said one ofsaid pair of conductive layers forming a potential pattern decreasingfrom the second region to the first region of said reflecting means.

5. An apparatus as recited in claim 4, wherein the development systemincludes magnetic means for depositing toner particles on theimage-bearing member, said magnetic means being electrically biased tosubstantially the same potential as the potential generated by saidfirst voltage source.

6. An apparatus as recited in claim 1, wherein:

said generating. means includes a light source; and

said detecting means includes a photosensor positioned to receive thelight rays reflected from said reflecting means.

7. An apparatus as recited in claiml, wherein said reflecting means ismounted on the image-bearing member. 1

8. An electrophotographic printing machine of the type having aphotoconductive member, and a development system employing a mix ofcarrier granules and V toner particles, the toner particles beingadapted to be deposited on an electrostatic latent image recorded on thephotoconductive member, wherein the improvement includes:

reflecting means disposed to attract toner particles thereto from thecarrier granules of the mix; means for biasing electrically saidreflecting means 'to produce a voltage pattern having a greaterpotential in a first region of said reflecting means than in a secondregion thereof; means for generating a beam of light ray, saidreflecting means being in a light-receiving relationship with the beamof light rays so that a third region thereof having a pre-selectedpotential intermediate the potential of the first region and secondregion is illuminated by the beam of light rays; and means for detectingthe intensity of the light rays reflected from said reflecting means,said detecting means producing an electrical output signal indicative ofthe intensity of light rays reflected from said reflecting means.

9. A printing machine as recited in claim 8, further including means,responsive to the electrical output signal from said detecting means,for dispensing toner particles into the mix of the development system tomaintain the concentration thereof substantially at the desired level.

10. A printing machine as recited in claim 8, wherein said reflectingmeans includes:

insulating support means;

a pair of conductive layers mounted on said support means, one of saidpair of conductive layers being positioned in the first region of saidreflecting means and the other of said pair of conductive layers beinglocated in the second region thereof; and

a resistance layer mounted on said support means connecting electricallysaid pair of conductive layers with one another.

11. A printing machine as recited in claim 10,

wherein said electricalbiasing means includes:

a first voltage source electrically coupled to said one of said pair ofconductive layers positioned in the first region of said reflectingmeans; and

a second voltage source electrically coupled to said other of said pairof conductive layers disposed in the second region of said reflectingmeans, said second voltage source generating a greater potential thanthe potential generated by sid first voltage source to create a currentflow from said other of said pair of conductive layers to said one ofsaid pair of conductive layers forming a potential pattern decreasingfrom the second region to the first region of said reflecting means.

12. A printing machine as recited in claim 11, wherein the developmentsystem includes magnetic means for depositing toner particles on theelectrostatic latent image recorded on the photoconductive member, saidmagnetic means being electrically biased to substantially the samepotential as the potential generated by said first voltage source.

13. A printing machine as recited in claim 8, wherein:

said generating means includes a light source; and

said detecting means includes a photosensor positioned to receive thelight rays reflected from said reflecting means.

14.. A printing machine as recited in claim 8, wherein said reflectingmeans is mounted on the photoconductive member.

15. An electrophotographic printing machine of the type having aphotoconductive member, and a development system employing a mix ofcarriergranules and toner particles, the toner particles being adaptedto be deposited on an electrostatic latent image recorded on thephotoconductive member, wherein the improvement includes:

means for forming on the photoconductive member a voltage gradienthaving the potential in a first region greater than the potential in asecond region so as to attract toner particles thereto from the carriergranules of the mix;

means for generating a beam of light rays, the voltage gradient formedon the photoconductive member being in a light-receiving relationshipwith the beam of light rays after toner particles are deposited thereonso that a portion thereof .having a preselected potential intermediatethe potential in the first region and the potential in the second regionis illuminated by the beam of light rays; and

means for detecting the intensity of the light rays reflected from thevoltage gradient formed on the photoconductive member, said detectingmeans producing an electrical output signal indicative of the intensityof light rays reflected from the illuminated portion of the voltagegradient formed on the photoconductive member. 16. A printing machine asrecited in claim 15, further including means, responsive to theelectrical output signal from said detecting means, for dispensing tonerparticles into the mix of the development system to maintain theconcentration thereof at substantially about the desired level. 1

17. A printing machine as recited in claim 16, wherein the developmentsystem includes magnetic means for depositing toner particles on thevoltage gradient formed on the photoconductive member, said magneticmeans being electrically biased to substantially the same potential asthe potential of the central region of the voltage gradient formed onthe photoconductive member.

18. A printing machine as recited in claim 17, wherein:

said generating means includes a light source; and said detecting meansincludes a photosensor positioned to receive the light rays reflectedfrom the sample electrostatic latent image recorded on thephotoconductive member.

19. A printing machine having a rotary journaled photoconductive memberas recited in claim 18, wherein said recording means produces a sampleelectrostatic latent image having a voltage gradient wherein thepotential of the voltage gradient decreases in the direction of rotationof the photoconductive member.

20. A printing machine as recited in claim 19, further including means,responsive to the electrical output signal from said detecting means,for dispensing toner particles into the mix of the development system tomaintain the concentration thereof at substantially about the desiredlevel.

21. A printing machine as recited in claim 20, wherein thedevelopmentsystem includes magnetic means for depositing toner particles on thesample electrostatic latent image recorded on the photoconductivemember.

22. A printing machine as recited in claim 21, wherein:

said generating means includes a light source; and

said detecting means includes a photosensor positioned to receive thelight rays reflected from the sample electrostatic latent image recordedon the photoconductive member.

1. An apparatus regulating toner particle concentration within a mix oftoner particles and carrier granules employed in a development systemarranged to deposit toner particles on an image-bearing member,including: reflecting means disposed to attract toner particles theretofrom the carrier granules of the mix; means for biasing electricallysaid reflecting means to produce a voltage pattern having a greaterpotential in a first region of said reflecting means than in a secondregion thereof; means for generating of a beam of light rays, saidreflecting means being in a light receiving relationship with the beamof lighT rays so that a third region thereof having a preselectedpotential intermediate the potential of the first region and secondregion is illuminated by the beam of light rays; and means for detectingthe intensity of the light rays reflected from said reflecting means,said detecting means producing an electrical output signal indicative ofthe intensity of light ray reflected from said reflecting means.
 2. Anapparatus as recited in claim 1, further including means, responsive tothe electrical output signal from said detecting means, for dispensingtoner particles into the mix of the development system to maintain theconcentration thereof at substantially about the desired level.
 3. Anapparatus as recited in claim 1, wherein said reflecting means includes:insulating support means; a pair of conductive layers mounted on saidsupport means, one of said pair of conductive layers being positioned inthe first region of said reflecting means and the other of said pair ofconductive layers being located in the second region thereof; and aresistance layer mounted on said support means connecting electricallysaid pair of conductive layers with one another.
 4. An apparatus asrecited in claim 3, wherein said electrical biasing means includes: afirst voltage source electrically coupled to said one of said pair ofconductive layers disposed in the first region of said reflecting means;and a second voltage source electrically coupled to said other of saidpair of conductive layers disposed in the second region of saidreflecting means, said second voltage source generating a greaterpotential than the potential generated by said first voltage source tocreate a current flow from said other of said pair of conductive layersto said one of said pair of conductive layers forming a potentialpattern decreasing from the second region to the first region of saidreflecting means.
 5. An apparatus as recited in claim 4, wherein thedevelopment system includes magnetic means for depositing tonerparticles on the image-bearing member, said magnetic means beingelectrically biased to substantially the same potential as the potentialgenerated by said first voltage source.
 6. An apparatus as recited inclaim 1, wherein: said generating means includes a light source; andsaid detecting means includes a photosensor positioned to receive thelight rays reflected from said reflecting means.
 7. An apparatus asrecited in claim 1, wherein said reflecting means is mounted on theimage-bearing member.
 8. An electrophotographic printing machine of thetype having a photoconductive member, and a development system employinga mix of carrier granules and toner particles, the toner particles beingadapted to be deposited on an electrostatic latent image recorded on thephotoconductive member, wherein the improvement includes: reflectingmeans disposed to attract toner particles thereto from the carriergranules of the mix; means for biasing electrically said reflectingmeans to produce a voltage pattern having a greater potential in a firstregion of said reflecting means than in a second region thereof; meansfor generating a beam of light ray, said reflecting means being in alight-receiving relationship with the beam of light rays so that a thirdregion thereof having a pre-selected potential intermediate thepotential of the first region and second region is illuminated by thebeam of light rays; and means for detecting the intensity of the lightrays reflected from said reflecting means, said detecting meansproducing an electrical output signal indicative of the intensity oflight rays reflected from said reflecting means.
 9. A printing machineas recited in claim 8, further including means, responsive to theelectrical output signal from said detecting means, for dispensing tonerparticles into the mix of the development system to maintain theconcentration thereof substantially at the desired level.
 10. A printingmachine as recited in claim 8, wherein said reflecting means includes:insulating support means; a pair of conductive layers mounted on saidsupport means, one of said pair of conductive layers being positioned inthe first region of said reflecting means and the other of said pair ofconductive layers being located in the second region thereof; and aresistance layer mounted on said support means connecting electricallysaid pair of conductive layers with one another.
 11. A printing machineas recited in claim 10, wherein said electrical biasing means includes:a first voltage source electrically coupled to said one of said pair ofconductive layers positioned in the first region of said reflectingmeans; and a second voltage source electrically coupled to said other ofsaid pair of conductive layers disposed in the second region of saidreflecting means, said second voltage source generating a greaterpotential than the potential generated by sid first voltage source tocreate a current flow from said other of said pair of conductive layersto said one of said pair of conductive layers forming a potentialpattern decreasing from the second region to the first region of saidreflecting means.
 12. A printing machine as recited in claim 11, whereinthe development system includes magnetic means for depositing tonerparticles on the electrostatic latent image recorded on thephotoconductive member, said magnetic means being electrically biased tosubstantially the same potential as the potential generated by saidfirst voltage source.
 13. A printing machine as recited in claim 8,wherein: said generating means includes a light source; and saiddetecting means includes a photosensor positioned to receive the lightrays reflected from said reflecting means.
 14. A printing machine asrecited in claim 8, wherein said reflecting means is mounted on thephotoconductive member.
 15. An electrophotographic printing machine ofthe type having a photoconductive member, and a development systememploying a mix of carrier granules and toner particles, the tonerparticles being adapted to be deposited on an electrostatic latent imagerecorded on the photoconductive member, wherein the improvementincludes: means for forming on the photoconductive member a voltagegradient having the potential in a first region greater than thepotential in a second region so as to attract toner particles theretofrom the carrier granules of the mix; means for generating a beam oflight rays, the voltage gradient formed on the photoconductive memberbeing in a light-receiving relationship with the beam of light raysafter toner particles are deposited thereon so that a portion thereofhaving a pre-selected potential intermediate the potential in the firstregion and the potential in the second region is illuminated by the beamof light rays; and means for detecting the intensity of the light raysreflected from the voltage gradient formed on the photoconductivemember, said detecting means producing an electrical output signalindicative of the intensity of light rays reflected from the illuminatedportion of the voltage gradient formed on the photoconductive member.16. A printing machine as recited in claim 15, further including means,responsive to the electrical output signal from said detecting means,for dispensing toner particles into the mix of the development system tomaintain the concentration thereof at substantially about the desiredlevel.
 17. A printing machine as recited in claim 16, wherein thedevelopment system includes magnetic means for depositing tonerparticles on the voltage gradient formed on the photoconductive member,said magnetic means being electrically biased to substantially the samepotential as the potential of the central region of the voltage gradientformed on the photoconductive member.
 18. A printing machine as recitedin claim 17, wherein: said generating means includes a light source; andsaid detecting means includes a photosensor positioned to receive thelight rays reflected from the sample electrostatic latent image recordedon the photoconductive member.
 19. A printing machine having a rotaryjournaled photoconductive member as recited in claim 18, wherein saidrecording means produces a sample electrostatic latent image having avoltage gradient wherein the potential of the voltage gradient decreasesin the direction of rotation of the photoconductive member.
 20. Aprinting machine as recited in claim 19, further including means,responsive to the electrical output signal from said detecting means,for dispensing toner particles into the mix of the development system tomaintain the concentration thereof at substantially about the desiredlevel.
 21. A printing machine as recited in claim 20, wherein thedevelopment system includes magnetic means for depositing tonerparticles on the sample electrostatic latent image recorded on thephotoconductive member.
 22. A printing machine as recited in claim 21,wherein: said generating means includes a light source; and saiddetecting means includes a photosensor positioned to receive the lightrays reflected from the sample electrostatic latent image recorded onthe photoconductive member.